Human performance in most visual tasks is known to reduce with age, with the rate of decline being task dependent. Here we investigated how performance in a multiple object tracking (MOT) task is affected by age. The stimuli consisted of 8 dots that moved along linear trajectories from left to right at a speed of 3.76 deg/s. At the midpoint of their trajectories, a certain number of dots, D (1, 2 or 3), deviated either clockwise or counter-clockwise by a certain magnitude (57°, 38° or 19°), and the task for observers was to identify the direction of deviation. Percent correct responses were measured for 22 observers aged 18 to 62 years (mean = 35.3 years, SD = 13.0 years) and these were converted to effective numbers of tracked trajectories (E) using techniques described in Tripathy, Narasimhan & Barrett (2007, Journal of Vision, 7:6:2:1–18). For each combination of D and magnitude of deviation tested, values of E were plotted against age and regression lines were fitted to the data. In 5 out of the 7 experimental conditions tested, the regression line had a significant negative slope, indicating an age-related decline in E. Furthermore, when performance was averaged across different values of D, there was a significant negative correlation between age and E for each of the three magnitudes of deviation tested. The rate of decline over the age-range tested was found to be equivalent to 0.38 trajectories per decade for deviations of ±57°, 0.36 trajectories per decade for ±38°, and 0.12 trajectories per decade for ±19°; this corresponds, approximately, to a 15% drop in performance for each decade of our adult lives. Performance in this tracking task begins to drop relatively early in adulthood, rather than remaining constant over much of adult life and then decreasing in middle or old age.